Alkaline primary battery

ABSTRACT

An alkaline primary cell which is improved in reduction of self-discharge and cell capacity under storage at a high temperature, has a prolonged life and makes use of nickel oxyhydroxide is provided inexpensively. β-Form nickel oxyhydroxide is contained in a positive electrode mixture as an active material, which contains cobalt and zinc as a substitutional element for solid solution, and has a total amount X+Y of molar ratios of cobalt atom X and zinc atom Y such that 2≦X+Y≦16, with a mixing ratio satisfying the relationship of Y≦3/2×X+1/2 and Y≧2/3×X −1/3, and where a diffraction peak obtained as a result of measurement of X-ray powder diffraction of nickel oxyhydroxide appears only in the vicinity of 18.5° within a range of 2θ=10°-30°.

TECHNICAL FIELD

The present invention relates to an alkaline primary cell having nickeloxyhydroxide to which at least cobalt and zinc alone are added as anactive material for positive electrode to a positive electrode mixturefor use as a solid solution substitutional element and moreparticularly, to an alkaline primary cell which is improved in dischargecharacteristics under high load and also in self-dischargecharacteristics under storage at high temperatures.

BACKGROUND ART

At present, alkaline manganese cells are now in main use as an alkalineprimary cell having high output characteristics, in which manganesedioxide is used as a positive electrode active material and zinc is usedas a negative electrode active material, with an alkaline aqueoussolution being employed as an electrolytic solution. In recent years, asportable appliances including digital cameras, information communicationterminals and the like are becoming high in performance, there is anincreasing demand for further improvement in high load characteristicsand also for high capacity in respect to alkaline manganese cells whichare used as a power source.

As a means which is capable of providing a cell having excellent outputcharacteristics in order to meet such a demand as mentioned above,attention has been long paid to application of nickel oxyhydroxide as apositive electrode active material, and studies have been, in fact, madethereon (see Japanese Patent Application Laid-open Publication Nos. Sho53-32347 and Sho 55-30133).

However, hitherto studied cells using nickel oxyhydroxide as a positiveelectrode active material have the problem that when the cells are leftover a long time under high temperature conditions, the cell capacitydecreases owing to self-discharge thereof, and thus have never been putinto practice. In particular, with primary cells, the reduction incapacity resulting from self-discharge means a loss of function as acell. Thus, it is essential to overcome the problem on the reduction ofcapacity ascribed to self-discharge in order to realize the practicaluse.

DISCLOSURE OF THE INVENTION

The invention has been accomplished under these circumstances and has anobject to provide an alkaline primary cell which overcomes the problemon the self-discharge caused during storage under high temperatureconditions with an accompanying problem on the reduction in cellcapacity, and which is capable of being stored over a long time with aprolonged life and makes use of nickel oxyhydroxide.

In order to achieve the above object, an alkaline primary cell accordingto one embodiment of the invention comprises a positive electrodemixture including nickel oxyhydroxide in which cobalt and zinc aloneused at least as an active material for positive electrode for use as asolid solution substitutional element, wherein, the nickel oxyhydroxide,a general formula of which being Ni_(1-x-y)Co_(x)Zn_(y)OOH, has thefollowing total amount X+Y of molar ratios of cobalt atom and zinc atomwhen the molar ratio of cobalt is represented by X and the molar ratioof zinc is represented by Y2 mole %≦X+Y≦16 mole %,

the molar ratio X of cobalt and the molar ratio Y of zinc, both servingas a solid solution substitutional element, satisfy the followingrelationshipY≦3/2×X+1/2Y≧2/3×X−1/3, anda diffraction peak obtained as a result of measurement of X-ray powderdiffraction of the nickel oxyhydroxide appears only in the vicinity of18.5° within a range of 2θ=10°-30°.

An alkaline primary cell according to a preferred embodiment of theinvention comprises a positive electrode mixture including nickeloxyhydroxide in which cobalt and zinc alone used at least as an activematerial for positive electrode for use as a solid solutionsubstitutional element, wherein, the nickel oxyhydroxide, a generalformula of which being Ni_(1-x-y)Co_(x)Zn_(y)OOH, has the followingtotal amount X+Y of molar ratios of cobalt atom and zinc atom when themolar ratio of cobalt is represented by X and the molar ratio of zinc isrepresented by Y4 mole %≦X+Y≦14 mole %,

the molar ratio X of cobalt and the molar ratio Y of zinc, both servingas a solid solution substitutional element, satisfy the followingrelationship,0.4≦X/(X+Y)≦0.6, and

a diffraction peak obtained as a result of measurement of X-ray powderdiffraction of the nickel oxyhydroxide appears only in the vicinity of18.5° within a range of 2θ=10°-30°.

The alkaline primary cell according to another embodiment of theinvention is characterized in that a molded article of the positiveelectrode active material is formed as a hollow cylinder, and a negativeelectrode active material is arranged at the center of the moldedarticle of the positive electrode active material with a separator putbetween the negative electrode active material and the molded articlethereby structuring an inside out type cell.

The invention is described in more detail below.

The present inventors have made studies and developments on solidsolution substitutional species contained in crystals, solid solutioncompositions, and cell arrangements in order to improve self-dischargereaction of nickel oxyhydroxide, and many experiments have beenconducted to obtain the following information, thus arriving atcompletion of the invention.

===Molar Ratios of Cobalt and Zinc===

It has been found that the reduction in capacity ascribed toself-discharge of nickel oxyhydroxide can be mitigated when cobalt andzinc alone are added as solid solution substitutional species, tocrystals and the ratio of cobalt and zinc satisfy the followingrelationshipY≦3/2×X+1/2Y≧2/3×X−1/3(wherein X: the number of cobalt atoms, and Y: the number of zincatoms).

Further, it has also been found that when the molar ratios of cobaltatom and zinc atom satisfy the following relationship,0.4≦X/(X+Y)≦0.6the effect of improving the self-discharge characteristics becomes moreapparent.===Total Amount of Solid Solution Substitutional Elements===

Where the total amount X+Y in substitutional solid solution of cobaltand zinc is lower than 2 mole %, the improving effect of self-dischargebecomes low and is thus unsuitable. Where the total amount X+Y of cobaltand zinc is larger than 16 mole %, the cell capacity is unsuitablylowered in association with the lowering in utilization rate of nickeloxyhydroxide.

Accordingly, the total amount X+Y in substitutional solid solution ofcobalt atom and zinc atom contained in nickel oxyhydroxide shouldpreferably be not less than 2 mole % and not larger than 16 mole % (2mole %≦X+Y≦16 mole %). The above effect is more significantly improvedwhen the total amount X+Y substitutional solid solution is more than 4mole % and less than 14 mole % (4 mole %≦X+Y≦14 mole %).

===Cell Arrangement===

In general, the cylindrical cell can be generally classified into aninside out type and a spiral type. The inside out type has such anarrangement that a negative electrode active material is disposedthrough a separator at the center of a molded article of a positiveelectrode active material in the form of a hollow cylinder. The spiraltype has a configuration where a layer built sheet structured by asheet-shaped positive electrode placed in face-to-face relation with asheet-shaped negative electrode through a separator is convolutely woundand inserted into a cell casing.

With the spiral type, it is necessary to use a current collectingsubstrate for structuring the sheet-shaped positive and negativeelectrode active materials. The use of current collecting substratesother than the active materials within a cell may invite a lowering inamount of active materials to be charged inside the cell having alimited capacity, and is thus unfavorable from the standpoint ofcapacity. The foamed nickel mesh and the like that is ordinarilyemployed as a current collecting substrate is very expensive, therebycausing cell costs to be increased.

From the standpoint of capacity and cost, the inside out type isdesirable for cell arrangement.

===Problems in a Case Using Nickel Hydroxide as an Active Material===

Generally, nickel hydroxide that serves as a positive electrode activematerial of nickel hydrogen secondary batteries, nickel cadmiumsecondary batteries and the like can be converted to nickel oxyhydroxideby electrochemical oxidation. However, the cell arrangement of theinside out type makes it difficult to ensure a good current collectingcondition. Accordingly, when an attempt has been made where nickelhydroxide is electrochemically oxidized while keeping the cellarrangement of the inside out type, a failure in current collection mayoccur within the active material for positive electrode partly due tothe influence that the electric conductivity of nickel hydroxide is low.In this way, a difficulty is involved in satisfactorily producing nickeloxyhydroxide throughout the positive electrode, thereby causing the cellcapacity to lower.

In a case where electrochemical oxidation is carried out excessively soas to increase the amount of formation of nickel oxyhydroxide, nickeloxyhydroxide in an excessively oxidized condition (hereinafter referredto as γ-form nickel oxyhydroxide) is formed along with β-form nickeloxyhydroxide which is assumed to be inherently formed.

This γ-form nickel oxyhydroxide has a wider interlayer distance thanβ-form nickel oxyhydroxide and causes the volumetric expansion ofpositive electrode active material to be induced in association with theformation of γ-form nickel oxyhydroxide. As a consequence, leakage takesplace, thus presenting a problem on safety.

Moreover, γ-form nickel oxyhydroxide exhibits great absorptivity ofelectrolytic solution, so that the formation of this compoundconstitutes a factor of causing shortage of electrolytic solution in thecell.

Accordingly, to maintain a good cell condition, mixing of γ-form nickeloxyhydroxide is not favorable.

Thus, in the cell arrangement of the inside out type, it is notpreferred to provide an active material by electrochemically oxidizingnickel hydroxide into nickel oxyhydroxide.

===Detection of γ-Form Nickel Oxyhydroxide===

The presence or absence of a γ-phase in nickel oxyhydroxide can beconfirmed by X-ray powder diffraction measurement as shown in FIG. 1.With β-form nickel oxyhydroxide, one diffraction spectrum is observed inthe vicinity of 18° within a range of 10-30° as a result of X-ray powderdiffraction. On the other hand, if γ-form nickel oxyhydroxide exists,two peaks are observed in the vicinity of 12.5° and 25.5°, respectively.Thus, the presence or absence of γ-form nickel oxyhydroxide can beconfirmed through the presence or absence of the peaks in the vicinityof 12.5° and at 25.5°.

It will be noted that the presence or absence of a γ phase in nickeloxyhydroxide may also be determined by measurement of acidity. If theacidity of nickel oxyhydroxide is larger than 3.0, a γ-form nickeloxyhydroxide phase exists. In this sense, the acidity of nickeloxyhydroxide used as an active material should preferably be at 3.0 orbelow. If the acidity is lower than 2.8, then oxidation into nickeloxyhydroxide is unsatisfactory, thereby causing the utilization rate asa cell active material to lower. Thus, the acidity of nickeloxyhydroxide should preferably be from 2.8 to 3.0.

===Method of Using β-form Nickel Oxyhydroxide Alone as an ActiveMaterial===

The problem of mixing such γ-form nickel oxyhydroxide in a positiveelectrode can be avoided when using, as an active material, nickeloxyhydroxide prepared by chemically oxidizing nickel hydroxidebeforehand. That is, the use of nickel oxyhydroxide prepared beforehandby chemical oxidation of nickel hydroxide enables one to obtain, in apositive electrode, a single phase of γ-form nickel oxyhydroxide-freeβ-form nickel oxyhydroxide.

===Chemical Oxidation Method===

The chemical oxidation into nickel oxyhydroxide is feasible by adding anoxidizing agent such as sodium hypochlorite to an alkaline aqueoussolution of nickel hydroxide being agitated and mixed.

The oxidizing agent is not limited to sodium hypochlorite, but allcompounds capable of converting nickel hydroxide into β-form nickeloxyhydroxide is usable.

===Summary===

The alkaline primary cell comprising, in a positive electrode mixture,single phase, β-form nickel oxyhydroxide which contains cobalt and zincalone as a substitutional solid solution species and in which a totalamount X+Y where X is a molar ratio of cobalt atom and Y is a molarratio of zinc atom is such that 2 mole %≦X+Y≦16 mole % and a mixingratio satisfies the following relationshipY≦3/2×X+1/2Y≧2/3×X−1/3suffers a reduced degree of degradation when stored at high temperatureover a long time, ensures a large capacity and can be provided at lowcosts.

It is preferred from the standpoint of realizing large capacity that theβ-form nickel oxyhydroxide has such a total amount of X+Y that 4 mole%≦X+Y≦14 mole % and a mixing ratio satisfying the followingrelationship:0.4≦X/(X+Y)≦0.6The cell is so arranged as to be of an inside out type where thepositive electrode mixture is inserted into a positive electrode can asa molded article of a hollow cylinder and a negative electrode activematerial is placed in the central portion of the cylinder with aseparator put between the negative electrode active material and themolded article, thus realizing low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the respective X-ray powder diffraction (XRD)patterns of γ-form nickel oxyhydroxide and β-form nickel oxyhydroxideused in the present invention;

FIG. 2 is a longitudinal sectional view of an alkaline primary cellaccording to the invention; and

FIG. 3 is a graph showing suitability concerning capacity retentionrates of alkaline primary cells of different types where cobalt and zincare formulated in nickel oxyhydroxide in different ratios with respectto the substitutional amount in solid solution of cobalt in nickeloxyhydroxide and the substitutional amount in solid solution of zinc innickel oxyhydroxide.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of an alkaline primary cell according to theinvention will be described with reference to the accompanying drawings.

First, conditions of preparing nickel oxyhydroxide containing cobalt andzinc alone as a substitutional solid solution species, fabrication ofcells for evaluation and characteristic evaluation testing conditionsare set forth below.

===Fabrication of Positive Electrode===

A sodium hydroxide aqueous solution was added to and agitated in areaction vessel in which 1000 ml of a mixed solution of nickel sulfate,cobalt sulfate and zinc sulfate having nickel, cobalt and zinc at givenatomic ratios, respectively, was maintained at 30° C. After agitationfor about 1 hour, the resultant precipitate was filtered out and washedwith water. After the washing, the sample was vacuum dried at a normaltemperature.

Next, 100 g of the resulting powder was added to 10 moles/liter of asodium hydroxide aqueous solution and agitated, followed by keeping thesolution temperature at 30° C. to 60° C. While agitating the solution,500 ml of a 10 wt % sodium hypochlorite aqueous solution was added toand agitated for about 1 hour. The resulting precipitate was removed byfiltration and washed with water, followed by vacuum drying at atemperature of 60° C. or below.

One hundred wt % of nickel oxyhydroxide containing only the cobalt andzinc obtained by the above procedure as a substitutional solid solutionspecies, 10 wt % of graphite powder and 5 wt % of a potassium hydroxideaqueous solution were mixed to prepare a mixture, followed by pressingto provide a hollow cylinder for use as a positive electrode.

===Fabrication of Negative Electrode===

One wt % of an acrylic resin was added to 60 wt % of a zinc powderprovided as a negative electrode active material and 40 wt % of apotassium hydroxide aqueous solution containing zinc oxide to saturationto provide gelled zinc for use as a negative electrode.

===Fabrication of Cell===

As shown in FIG. 3, the above positive electrode molding 2 is insertedin contact within a cell can 4 in the form of a hollow cylinder with abottom, and a separator 6 made of a polypropylene non-woven fabricprocessed in the form of a cylinder is placed on the inner side of thepositive electrode molding 2, followed by placing a negative electrode 8at the central portion inside the separator 6.

The opening of the cell can 4 was hermetically sealed by use of aterminal 16 for the negative electrode which was made integrally of acurrent collector 10, a gasket 12 and a negative electrode cover 14,thereby obtaining an intended cell.

===Evaluation Test of Storage Characteristics===

Ten cells for each of the formulations where mixing ratios of therespective positive electrode active materials were taken as X mole % ofcobalt and Y mole % of zinc were widely changed, and fabricated. Fivecells among them were discharged to 0.9 V through 1 W constant powerdischarge immediately after the fabrication and an average value ofdischarge duration times of the respective cells was calculated toprovide an initial discharge duration time.

The other five cells among the pre-production samples were stored at 60°C. for 20 days, after which they were allowed to be discharged to 0.9 Vthrough 1 W constant power discharge, and an average value of dischargeduration times of the respective cells was calculated to provide adischarge duration time after the storage.

For the value indicating a characteristic degradation after storage ofthe cell, a value of capacity retention rate was defined according tothe following equation for comparison.

Capacity retention rate=(discharge duration time afterstorage×100)/initial discharge duration time

Tables 1 and 2 show the correlation of the alkaline primary cells havingdifferent mixing ratios between the substitutional amount in solidsolution of cobalt and the substitutional amount in solid solution ofzinc in nickel oxyhydroxide in relation to the capacity retention ratethereof. FIG. 3 is a graph obtained by plotting the results of Tables 1and 2 and showing a range of acceptance or rejection. As will beapparent from these Tables 1 and 2 and the graph of FIG. 3, withExamples A1 to A19 and B1 to B6 where the total amount X+Y where thesubstitutional amount in solid solution of cobalt atom is taken as Xmole % and the substitutional amount in solid solution of zinc atom istaken as Y mole % is within a range of 2 mole %≦X+Y≦16 mole % and themixing ratio is such that Y≦3/2×X+1/2 and Y≧2/3×X−1/3, the capacityretention rate can be kept at 60% or over. In contrast, with ComparativeExamples a1, b1 and b2 where the total amount X+Y is outside the aboverange and also with Comparative examples a2 to a8 and b1 to b2 where theabove-defined mixing ratio does not satisfy the requirement of{(2/3×X−1/3)≦Y≦(3/2×X+1/2)}, the capacity retention rate is less than60%.

With the case where the total amount X+Y is within a range of 4 mole%≦X+Y≦14 mole % and the mixing molar ratio between cobalt atom and zincatom satisfies the relation of 0.4≦X/(X+Y)≦0.6 (Examples A1, A2, A3, A6,A8, A10, A11, A14, A15, A16, A17, B2, B3, B4 and B5), the capacityretention rate reaches 69% or more and is thus remarkably improved.

TABLE 1 Substitutional Substitutional amount in amount solid in solidsolution solution Capacity of cobalt of zinc Retention UtilizationX/mole % Y/mole % X + Y X/(X + Y) Rate Rate Judgment Example A1 5 4 90.56 74 90 ⊚ Example A2 5 5 10 0.5 75 90 ⊚ Example A3 5 6 11 0.45 70 87⊚ Example A4 5 8 13 0.38 65 83 ◯ Example A5 5 3 8 0.63 63 89 ◯ ExampleA6 3 2 5 0.6 69 93 ⊚ Example A7 3 5 8 0.38 66 90 ◯ Example A8 3 4 7 0.4371 91 ⊚ Example A9 8 5 13 0.62 62 84 ◯ Example A10 6 4 10 0.6 69 90 ⊚Example A11 4 6 10 0.4 70 85 ⊚ Example A12 0.6 1.4 2 0.3 64 99 ◯ ExampleA13 1.4 0.6 2 0.7 61 99 ◯ Example A14 6.2 9.8 16 0.39 66 80 ◯ ExampleA15 9.8 6.2 16 0.61 61 80 ◯ Example A16 1.6 2.4 4 0.4 69 95 ⊚ ExampleA17 2.4 1.6 4 0.6 69 97 ⊚ Example A18 5.6 8.4 14 0.4 69 83 ⊚ Example A198.4 5.6 14 0.6 61 85 ◯ Comparative 0 0 0 — 40 100 X example a1Comparative 5 0 5 1 30 96 X example a2 Comparative 5 2 7 0.71 45 93 Xexample a3 Comparative 5 10 15 3 35 70 X example a4 Comparative 3 6 9 343 85 X example a5 Comparative 8 4 12 0.66 54 80 X example a6Comparative 10 0 10 1 48 70 X example a7 Comparative 0 10 10 0 40 68 Xexample a8

TABLE 2 Substitutional Substitutional amount in amount in solid solidsolution of solution Capacity cobalt of zinc Retention UtilizationX/mole % Y/mole % X + Y X/(X + Y) Rate Rate Judgment Example B1 1 1 20.5 62 98 ◯ Example B2 2 2 4 0.5 70 96 ⊚ Example B3 3 3 6 0.5 73 93 ⊚Example B4 6 6 12 0.5 75 89 ⊚ Example B5 7 7 14 0.5 70 85 ⊚ Example B6 88 16 0.5 67 82 ◯ Comparative 0.5 0.5 1 0.5 45 99 X example b1Comparative 9 9 18 0.5 58 68 X example b2===Specific Surface Area===

The results of a study on the specific surface area of nickeloxyhydroxide where cobalt and zinc alone were subjected to substitutionin solid solution, revealed that in order to reduce self-discharge understorage at high temperature, it was preferable to use an active materialhaving a specific surface area of 30 m²/g or less. More specifically,with respect to nickel oxyhydroxide where the substitutional amounts insolid solution of cobalt and zinc were, respectively, 5 mole %, thespecific surface area was set at three levels of 35 m²/g (Example C1),30 m²/g (Example C2), and 15 m²/g (Example C3), to compare therespective capacity retention rates, with the following results shown inTable 3. It was found that where the specific surface area was largerthan 30 m²/g, the capacity retention rate under storage at a hightemperature became lower than 70%, unfavorably resulting in increase ofself-discharge. It will be noted that the specific surface area wasmeasured according to the BET method.

TABLE 3 Substitutional Substitutional amount in amount in solid solidSpecific Capacity solution of solution of surface retention cobalt zincarea rate Judg- X/mole % Y/mole % (m²/g) (%) ment Exam- 5 5 35 60 ◯ pleC1 Exam- 5 5 30 70 ⊚ ple C2 Exam- 5 5 15 75 ⊚ ple C3===Mixing of Manganese Dioxide===

For a positive electrode active material, manganese dioxide that isordinarily used as a positive electrode active material of an existingalkaline cell may be contained in addition to nickel oxyhydroxide.

More specifically, a product obtained by subjecting 5 mole % of cobaltand 5 mole % of zinc to substitutional solid solution treatment wasprovided as nickel oxyhydroxide, and the capacity retention rates andcell capacities of cells using 100% of the above nickel oxyhydroxide(Example D1), mixtures with manganese dioxide at mixing ratios of 75:25(Example D2), 50:50 (Example D3) and 25:75 (Example D4), and 100% ofmanganese dioxide (Comparative Example d1) were compared with oneanother, with the results shown in Table 4 below. In Table 4, the cellcapacity is indicated as a relative value in a case where the capacityof the cell using 100% of nickel oxyhydroxide is taken as 100. It willbe noted that discharge conditions include 1 W constant power dischargeand a final voltage is at 1 V.

As shown in Table 4, although the capacity retention rates are equal toone another for all the cases, the cell capacity reliably increases asthe mixing ratio of nickel oxyhydroxide increases. Thus, addition ofnickel oxyhydroxide to manganese dioxide permits the capacity of analkaline primary cell to be reliably increased.

TABLE 4 Capacity Amount of Amount of retention Cell capacity NiOOH/wt %MnO₂/wt % rate (relative value) Example D1 100 0 75 100 Example D2 75 2575 88 Example D3 50 50 75 78 Example D4 25 75 75 68 Comparative 0 100 7550 example d1===Combination with Other Types of Metals===

As shown in Comparative Examples e1 to e13 shown in Tables 5, 6 and 7below, combinations with other types of metals such as aluminum,titanium, calcium, magnesium aside from cobalt and zinc for use as asubstitutional element for solid solution of nickel oxyhydroxide werechecked, with the result that any of those combinations other than acombination of cobalt and zinc alone were not suitable because thecapacity retention rate could not exceed 60%.

TABLE 5 Capacity Solid solution retention Utilization composition raterate Judgment Comparative Co 5 mol % + Al 48 65 X example e1 5 mol %Comparative Co 5 mol % + Ti 45 45 X example e2 5 mol % Comparative Co 5mol % + Ca 50 48 X example e3 5 mol % Comparative Co 5 mol % + Mg 50 50X example e4 5 mol %

TABLE 6 Capacity Solid solution retention Utilization composition raterate Judgment Comparative Zn 5 mol % + Al 45 50 X example e5 5 mol %Comparative Zn 5 mol % + Ti 47 40 X example e6 5 mol % Comparative Zn 5mol % + Ca 48 45 X example e7 5 mol % Comparative Zn 5 mol % + Mg 50 45X example e8 5 mol %

TABLE 7 Capacity Solid solution retention Utilization Judg- compositionrate rate ment Comparative Co 5 mol % + Zn 50 60 X example e9 5 mol % +Al 5 mol % Comparative Co 5 mol % + Zn 40 50 X example e10 5 mol % + Ti5 mol % Comparative Co 5 mol % + Zn 53 70 X example e11 5 mol % + Mn 5mol % Comparative Co 5 mol % + Zn 45 50 X example e12 5 mol % + Ca 5 mol% Comparative Co 5 mol % + Zn 40 55 X example e13 5 mol % + Mg 5 mol %

INDUSTRIAL APPLICABILITY

As having described in detail hereinabove, an alkaline primary cell ofthe present invention comprising, in a positive electrode mixture,single phase, β-form nickel oxyhydroxide which contains cobalt and zincalone as a substitutional solid solution species and where a totalamount X+Y in which a molar ratio of cobalt atom is taken as X and amolar ratio of zinc atom is taken as Y, such that 2≦X+Y≦16, and a mixingratio satisfies the following relationshipsY≦3/2×X+1/2Y≧2/3×X−1/3exhibits a reduced degree of degradation caused by self-discharge whenstored at high temperature over a long time, ensures a high capacity andcan be provided at low costs.

More preferably, when the single phase, β-form nickel oxyhydroxide has atotal amount X+Y of 4 mole %≦X+Y≦14 mole %, with the mixing ratiothereof satisfying the following relation0.4≦X/(X+Y)≦0.6a more remarkably improved capacity and capacity retention rate can berealized.

Moreover, when the positive electrode mixture is provided as a moldingof a hollow cylinder and inserted into a positive electrode case, and anegative electrode active material is arranged at the center of themolding with a separator put between the negative electrode activematerial and-the molding to provide an inside out type of cell, lowercosts can be realized.

1. An alkaline primary cell comprising a positive electrode mixtureincluding nickel oxyhydroxide in which cobalt and zinc alone used atleast as an active material for a positive electrode for use as asubstitutional element for solid solution, wherein, said nickeloxyhydroxide, a general formula of which beingNi_(1-x-y)Co_(x)Zn_(y)OOH, has the following total amount X+Y of molarratios of cobalt atom and zinc atom when the molar ratio of cobalt isrepresented by X and the molar ratio of zinc is represented by Y2 mole %≦X+Y≦16 mole %, the molar ratio X of cobalt and the molar ratioY of zinc, both serving as a solid solution substitutional element,satisfy the following relationshipY≦3/2×X+1/2Y≧2/3×X−1/3, and a diffraction peak obtained as a result of measurementof X-ray powder diffraction of said nickel oxyhydroxide appears only inthe vicinity of 18.5° within a range of 2θ=10°-30°.
 2. An alkalineprimary cell comprising a positive electrode mixture including nickeloxyhydroxide in which cobalt and zinc alone used at least as an activematerial for positive electrode for use as a substitutional element forsolid solution, wherein, said nickel oxyhydroxide, a general formula ofwhich being Ni_(1-x-y)Co_(x)Zn_(y)OOH, has the following total amountX+Y of molar ratios of cobalt atom and zinc atom when the molar ratio ofcobalt is represented by X and the molar ratio of zinc is represented byY4 mole % ≦X+Y≦14 mole %, the molar ratio X of cobalt and the molar ratioY of zinc, both serving as a solid solution substitutional element,satisfy the following relationship,0.4≦X/(X+Y)≦0.6, and a diffraction peak obtained as a result ofmeasurement of X-ray powder diffraction of the nickel oxyhydroxideappears only in the vicinity of 18.5° within a range of 2θ=10°-30°. 3.An alkaline primary cell according to claim 1 wherein a molding of saidpositive electrode active material is formed as a hollow cylinder, and anegative electrode active material is arranged at the center of saidmolding of said positive electrode active material with a separator putbetween said molding and the negative electrode active material.
 4. Analkaline primary cell according to claim 2, wherein a molding of saidpositive electrode active material is formed as a hollow cylinder, and anegative electrode active material is arranged at the center of saidmolding of said positive electrode active material with a separator putbetween said molding and the negative electrode active material.